Calibration of ultrasound probes

ABSTRACT

A method of calibrating an ultrasound probe includes mounting an ultrasound probe onto a calibration system, transmitting an ultrasound test signal from an element of the probe through a test medium of the calibration system, and receiving the test signal on a matrix of hydrophones such that an element&#39;s position relative to other elements and other arrays within the same probe can be computed. Further, the system described herein is configured to detect the acoustic performance of elements of a probe and report the results to an end user or service provider.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 13/279,110,filed Oct. 21, 2011, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/760,327, filed Apr. 14, 2010, now U.S. Pat. No.8,473,239, which claims the benefit of U.S. Provisional PatentApplication No. 61/169,200, filed Apr. 14, 2009, titled “Alignment andFixturing of the Universal Multiple Aperture Medical UltrasoundTransducer”. All of the above referenced patents and applications areincorporated herein by reference in their entireties.

This application is relevant to Applicant's co-owned patent applicationsincluding U.S. patent application Ser. No. 12/760,375, filed Apr. 14,2010, titled “Universal Multiple Aperture Medical Ultrasound Probe”,published Oct. 14, 2010 as U.S. Patent Publication No. 2010-0262013, andU.S. Provisional Patent Application No. 61/392,896, filed Oct. 13, 2010,titled “Multiple Aperture Medical Ultrasound Transducers.” All of theabove referenced patents and applications are incorporated herein byreference in their entireties.

INCORPORATION BY REFERENCE

Unless otherwise specified herein, all patents, publications and patentapplications mentioned in this specification are herein incorporated byreference to the same extent as if each individual publication or patentapplication was specifically and individually indicated to beincorporated by reference.

FIELD

The present invention relates generally to imaging techniques, and moreparticularly to ultrasound imaging, and still more particularly tosystems and methods for calibration and quality assurance measurement ofultrasound probes, particularly probes having multiple apertures.

BACKGROUND

In conventional ultrasonic imaging, a focused beam of ultrasound energyis transmitted into body tissues to be examined and the returned echoesare detected and plotted to form an image. While ultrasound has beenused extensively for diagnostic purposes, conventional ultrasound hasbeen greatly limited by depth of scanning, speckle noise, poor lateralresolution, obscured tissues and other such problems.

Significant improvements have been made in the field of ultrasoundimaging with the creation of multiple aperture imaging, examples ofwhich are shown and described in Applicant's U.S. Pat. No. 8,007,439issued Aug. 30, 2011 and titled “Method and Apparatus to ProduceUltrasonic Images Using Multiple Apertures”; U.S. Pat. No. 9,146,313issued Sep. 29, 2015, titled “Point Source Transmission andSpeed-Of-Sound Correction Using Multiple-Aperture Ultrasound Imaging”;and U.S. patent application Ser. No. 12/760,375, filed Apr. 14, 2010,titled “Universal Multiple Aperture Medical Ultrasound Probe,” all threeof which are incorporated herein by reference. Multiple aperture imagingmethods and systems allow for ultrasound signals to be both transmittedand received from separate apertures.

One problem with multiple aperture imaging is that it can be difficultto know the exact position of the elements of a large apparatus withmultiple and separate physical points of contact (“footprints”) on thepatient. It is desirable for each element position to be known to within1/10 wavelength (for example, 0.03 mm at 3 MHz). In contrast, withconventional ultrasound probes, regardless of array verticaldisplacement or integration (e.g., 1.5D or 2D), there has never been aneed to solve alignment and position issues between multiple arrays ormultiple individual elements. The calibration methods and apparatusesdescribed herein teach how to solve these problems for UniversalMultiple Aperture ultrasound probes.

SUMMARY

In general, in one aspect, a method of calibrating an ultrasound probeincludes mounting an ultrasound probe onto a calibration system,transmitting an ultrasound test signal from an element of the probethrough a test medium of the calibration system, receiving the testsignal at a first hydrophone of the calibration system at a first time;receiving the test signal at a second hydrophone of the calibrationsystem at a second time, receiving the test signal at a third hydrophoneof the calibration system at a third time, and determining an acousticposition of the element based upon differences in the first time, thesecond time, and the third time.

This and other embodiments may include one or more of the followingfeatures.

The elements can be part of an array having a plurality of elements, andthe method can further include repeating the transmitting, receiving,and determining steps for at least one additional element in the array.The transmitting, receiving, and determining steps can be performed forevery element in the array. The transmitting, receiving, and determiningsteps can be performed for less than all of the elements in the array,and the method can further include interpolating acoustic positions ofall remaining elements. The probe can include a plurality of distinctarrays, and the transmitting, receiving, and determining steps can beperformed for at least two elements in each array. The plurality ofarrays can be separated by physical space. At least one array can benon-planar with respect to another array.

The first, second, and third hydrophones can be part of a first line ofhydrophones and fourth, fifth, and sixth hydrophones can be part of asecond line that is parallel to the first line, and the method canfurther include receiving the test signal on all six hydrophones anddetermining an x, y, and z position of the element based on differencesof arrival times at each hydrophone. Further, there can be a third lineof two or more hydrophones that is transverse to the first and secondlines, and the method can further include computing the angle oftransmission of the element based upon the position of maximum levels ofenergy received on any of the hydrophones.

The method can further include storing the determine position of theelement in a memory chip on the probe. The method can further includeoverwriting position data stored in a memory chip with the determinedposition.

The method can further include establishing a tank coordinate systemrelative to the first, second, or third hydrophone. The method canfurther include determining a position of every element of the proberelative to the tank coordinate system. The method can further includeestablishing a probe coordinate system relative to an element of theprobe. The method can further include rotating or translating all of thedetermined positions to the probe coordinate system. The position can bedetermined relative to a Cartesian coordinate system.

The method can further include storing the determined position in memoryand retrieving the stored position during imaging or image processing.

The method can further include transmitting an ultrasound test signalfrom a fourth hydrophone to the first, second, or third hydrophone toverify the operation of the first, second, or third hydrophone.

In general, in one aspect, a method of determining functionality of anultrasound probe can include mounting an ultrasound probe onto acalibration system, transmitting an ultrasound signal between ahydrophone of the calibration system and an element of the probe, thetransmitting occurring through test medium of the calibration system;and determining an acoustic performance of the element.

This and other embodiments can include one or more of the followingfeatures.

The test signal can be transmitted from the hydrophone and received bythe element. The test signal can be transmitted from the element andreceived by the hydrophone.

The element can be part of an array having a plurality of elements, andthe method can further include repeating the transmitting, receiving,and determining steps for at least one additional element in the array.The probe can include a plurality of distinct arrays, and thetransmitting, receiving, and determining steps can be performed for atleast one element of each array.

The test signal can be transmitted by the first, second, or thirdhydrophone and received by a fourth hydrophone to verify signalperformance.

The determined acoustic performance can be stored and transmittedelectronically to report probe performance to service providers and endusers.

In general, in one aspect, a system for calibrating an ultrasound probeincludes a tank substantially filled with a test medium, a dock attachedto the tank, and a plurality of hydrophones. The dock is configured tohold an ultrasound probe. The plurality of hydrophones are arranged in amatrix along a wall of the tank opposite the dock.

This and other embodiments can include one or more of the followingfeatures.

The system can further include a controller configured to send anultrasound signal from an element of the probe through the test mediumto first, second, and third hydrophones of the plurality of hydrophones,and the controller can be further configured to determine an acousticposition of the element based upon differences in times that the signalis received at the first, second, and third hydrophones.

The system can further include the probe, and the probe can include atleast two arrays separated by a physical space, and the dock can beconfigured so as to hold at least one of the arrays at a non-orthogonalangle with respect to the hydrophone matrix. The probe can include acalibration memory chip configured to store data obtained by thecalibration system.

The dock can be configured to conform to the ultrasound probe shape. Thedock can be configured such that, when the probe is positioned in thedock, the probe is directly adjacent to the test medium. The material ofthe dock can have substantially the same speed of sound as the testmedium.

The matrix can include a first row of hydrophones, a second row ofhydrophones parallel to the first row of hydrophones, and a third row ofhydrophones transverse to the first and second rows.

The system can further include a calibrator hydrophone located on a wallof the tank separate from the wall along which the plurality ofhydrophone receivers are arranged.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a two-aperture system.

FIG. 2 illustrates a three-aperture system.

FIG. 3 is a schematic diagram showing a possible fixture for positioningan omni-directional probe relative to the main probe.

FIG. 4 is a schematic diagram showing a non-instrumented linkage for twoprobes.

FIG. 5 is a block diagram of the transmit and receive functions where athree array Multiple Aperture Ultrasound Transducer and the associatedMAUI electronics are used in conjunction with a host ultrasound machine.In this embodiment, the center probe is used for transmit only andmimics the normal operation of the host transmit probe.

FIG. 5A is a block diagram of the transmit and receive functions where atwo array Multiple Aperture Ultrasound Transducer and the associatedMAUI electronics are used as an add-on to a host ultrasound machine,primarily for cardiac applications, with an add-on instrument. In thiscase, one probe is used for transmit only and mimics the normaloperation of the host transmit probe, while the other probe operatesonly as a receiver.

FIG. 6 is a block diagram of the transmit and receive functions where aMultiple Aperture Ultrasound Transducer is used in conjunction with onlya Multiple Aperture Ultrasonic Imaging (MAUI) device. The stand-aloneMAUI electronics control all elements on all apertures. Any element maybe used as a transmitter or omni-receiver, or grouped into transmit andreceive full apertures or even sub-arrays. In this figure theinsonification emanates from the central aperture, aperture 2 of 3apertures.

FIG. 6A depicts the insonification emanating from other than centeraperture, in this figure Aperture 3 of 3.

FIG. 6B is an illustration of two apertures being used a MultipleAperture Ultrasound Transducer is used in conjunction with only aMultiple Aperture Ultrasonic Imaging (MAUI) device. In this figure theinsonification emanates from aperture 2 of 2.

FIG. 6C is an illustration of two apertures being used a MultipleAperture Ultrasound Transducer is used in conjunction with only aMultiple Aperture Ultrasonic Imaging (MAUI) device. In this figure theinsonification emanates from aperture 1 of 2.

FIG. 7A is a top view of the precision array carrier with six adjustmentscrews and an array installed.

FIG. 7B is a side view showing the longitudinal axis adjustment of anarray in the precision array carrier being supported by thearray-centering gasket.

FIG. 7C is an end view showing the transverse axis adjustment of thearray in the precision array carrier being supported by thearray-centering gasket.

FIG. 8A is a top view of the precision array carrier.

FIG. 8B is a side (longitudinal) view of the precision array carrier.

FIG. 8C is an end (lateral) view of the precision array carrier.

FIG. 9A is a top view of the precision array carrier with a centeringgasket in place.

FIG. 9B is a side view (longitudinal) of the precision array carrierwith a centering gasket in place.

FIG. 9C is an end view (lateral) the precision array carrier with acentering gasket in place.

FIG. 9D is a bottom view of the precision array carrier with a centeringgasket in place.

FIG. 10A is a top view of the array in the precision array carrierduring a counter-clockwise rotational axis adjustment.

FIG. 10B is a top view of the array in the precision array carrierduring a clockwise rotational axis adjustment.

FIG. 11 shows an end view of a precision array carrier 2150 installed ona tissue equivalent phantom 2182 and ready to transmit and receiveduring alignment.

FIG. 12 shows a side view of the phantom 2182 with the ends of thetargets 2167 visible.

FIG. 13A is a top view of a carrier assembly with arrays installed (tobecome a precision carrier array assembly) and aligned within aprecision transducer receptacle and stabilized with an acoustic dampingmaterial.

FIG. 13B is a side view of a precision array carrier with arraysinstalled (to become a precision carrier array assembly) and alignedwithin a precision transducer receptacle and stabilized with an acousticdamping material.

FIG. 13C is an end view of a precision carrier array with arraysinstalled (to become a precision carrier array assembly) and alignedwithin a precision transducer receptacle and stabilized with an acousticdamping material.

FIG. 14A is a top view of a precision carrier array with arraysinstalled and aligned within a precision transducer head receptacle, theacoustic damping material has set and alignment screws have beenremoved.

FIG. 14B is a side view of a precision carrier array assembly witharrays installed and aligned within a precision transducer headreceptacle, the acoustic damping material has set and alignment screwshave been removed.

FIG. 14C is an end view of a precision carrier array with arraysinstalled and aligned within a precision transducer head receptacle, theacoustic damping material has set and alignment screws have beenremoved.

FIG. 15 shows a precision transducer receptacle or nose piece and threeprecision carrier array assemblies seated atop the transducer guides.

FIG. 16 shows the precision transducer receptacle or nose piece andthree precision carrier array assemblies as in FIG. 22, and anultrasound transducer array seated in each transducer guide of the nosepiece.

FIG. 17 is a drawing using three independent probes and their installedarrays or transducers. This illustration represents the positionalnomenclature and array element numbering conventions.

FIG. 18A shows the Precision Stage Assembly and sections that controlmovement in three different axes.

FIG. 18B shows the controls for the Precision Stage Assembly.

FIG. 19A depicts is an enclosure containing Right and Left AxialHydrophones and a Transverse Hydrophone.

FIG. 19B depicts the dual Axial Hydrophones from the side andillustrates the angular orientation of the Transverse Hydrophone.

FIG. 20 is a representation of probes attached to the precision stageassemblies on top of a fluid filled tank, and well above the hydrophoneassembly.

FIG. 21A is a graphic of basic geometry used to begin the conversion ofdistance difference into total distance.

FIG. 21B is a graphic of the detailed geometry used to begin theconversion of distance difference into total distance allowing for theprecision location of array element using three hydrophones.

FIG. 21C is a graphic of geometry used to compute the z position of anelement.

FIG. 22 illustrates a nose piece containing three separate arrays afterit is installed into a Multiple Aperture Transducer. This figureincludes the transducer specific calibration chip, the transmitsynchronization module and probe position displacement sensor.

FIG. 23A is a representation of the graphical user interface or GUIdeveloped to allow for the precise location of elements of multiplearrays under test.

FIG. 23B depicts an array of elements under test with the ultrasoundbeam in the center of the transverse hydrophone, centered between theleft and right hydrophones with the results displayed on the graphicaluser interface.

FIG. 23C is a representation of an array under test where its beam is oncenter but with the array to the right of center with the resultsdisplayed on the graphical user interface.

FIG. 23D is a representation of an array under test that is physicallyon the center axis, but has its beam is to the left of center with theresults displayed on the graphical user interface.

FIG. 24 is a representation of the automatic precision stage assemblyand its major components.

FIG. 25 is a representation using three arrays and three precisionalignment stage assemblies showing their physical placement duringtesting.

FIG. 26A is an illustration of an Onboard Calibration and QualityAssurance fixture mounted to the side of the MAUI standalone system.This illustration depicts a MAUI Radiology probe being evaluated.

FIG. 26B illustrates the Onboard Calibration and Quality Assurancefixture evaluating a MAUI Cardiac probe.

FIG. 27A is a perspective view illustrating an embodiment of acalibration system attached to a multiple aperture ultrasound imaging(MAUI) control panel.

FIG. 27B illustrates an embodiment of a calibration system built into aMAUI electronics control panel.

FIG. 28 represents a side section view of a calibration system.

FIG. 29A illustrates a multiple aperture probe containing three separatearrays This figure includes a transducer specific calibration chipmounted within the probe handle.

FIG. 29B illustrates an embodiment of a curvilinear multiple apertureultrasound imaging probe.

FIG. 30A is a bottom view of a 1D or 1.5D ultrasound transducer array.

FIG. 30B is a perspective view of a single 1D or 1.5D ultrasoundtransducer element with a longitudinal geometric centerline shown.

FIG. 30C is a bottom view of a 2D matrix ultrasound transducer array.

FIG. 30D is a bottom view of a CMUT ultrasound transducer array.

FIG. 31 illustrates an embodiment of a calibration system with anadjustable clasp retaining one embodiment of a MAUI probe in a dockingsite which may contain a coupling gel.

FIG. 32A shows the top view of an embodiment of a calibration systemcontaining a removable docking site which contains multiple dockingforms for various shapes and types of probes.

FIG. 32B shows a side view illustrating an embodiment of a calibrationsystem containing a removable docking site having three differentdocking forms for receiving ultrasound probes.

FIG. 33A shows a side section view of an embodiment of a calibrationsystem with a removable docking site with a single docking form forreceiving an ultrasound probe.

FIG. 33B is a section view illustrating three embodiments of dockingforms for curvilinear, linear and trans-esophageal ultrasound probes.

FIG. 34A is a plan view illustration of one embodiment of a hydrophonematrix which may be located at a bottom of a calibration system.

FIG. 34B a side view of the hydrophone matrix of FIG. 34A.

DETAILED DESCRIPTION

The following disclosure provides embodiments of calibration systems andrelated operation methods for calibrating ultrasound imaging probes, andparticularly multiple aperture ultrasound imaging (MAUI) probes.Embodiments herein also provide systems and methods for operating such acalibration system for various purposes relating to quality assurance ofthe probes.

In some embodiments, a calibrating system may be configured to identifythe location of each and every individual element in an ultrasound probeto a high degree of accuracy and precision. In probes having multiplearrays of transducer elements, a calibration system may be configured toidentify the location and/or orientation of individual arrays. In otherembodiments, a calibration system may be configured to identify thelocation of only selected elements of one or more arrays. In someembodiments, the location of elements and/or arrays may be determined ina three dimensional space such as a given X, Y, and Z coordinate system.In other embodiments, the location of elements and/or arrays may bedetermined in only two dimensions, such as an X, Y coordinate systemwhich may correspond to an imaging plane of the probe.

As used herein, references to the “exact” or “precise” position oftransducer elements (and similar terms) may imply a relatively tighttolerance. For example, in some embodiments ultrasound probe calibrationsystems and methods may provide information describing the acousticposition of each transducer element in an array to within a distance ofa fraction of a wavelength of ultrasound being used. In someembodiments, the acoustic position of transducer elements may bedetermined to within 1/10 of a wavelength. In other embodiments, theacoustic position of transducer elements may be determined to within atolerance of less than 1/10 of a wavelength. In some embodiments, suchas for calibrating a standard (i.e., single aperture) ultrasound probe,much looser tolerances may also be used, provided that such tolerancesmeet the needs of a particular system.

The simplest multi-aperture system consists of two apertures, as shownin FIG. 1. One aperture could be used entirely for transmit elements 110and the other for receive elements 120. Transmit elements can beinterspersed with receive elements, or some elements could be used bothfor transmit and receive. In this example, the probes have two differentlines of sight to the tissue to be imaged 130. That is, they maintaintwo separate physical apertures on the surface of the skin 140. MultipleAperture Ultrasonic Transducers are not limited to use from the surfaceof the skin, they can be used anywhere in or on the body to includeintracavity and intravenous probes. In transmit/receive probe 110, thepositions of the individual elements T_(x) 1 through T_(x)n can bemeasure in three different axes. This illustration shows the probeperpendicular to the x axis 150, so each element would have a differentposition x and the same position y on the y axis 160. However, the yaxis positions of elements in probe 120 would be different since it isangled down. The z axis 170 comes in or out of the page and is verysignificant in determine whether an element is in or out of the scanplane.

Referring to FIG. 1, suppose that a Transmit Probe containing ultrasoundtransmitting elements T1, T2, . . . Tn 110 and a Receive Probe 120containing ultrasound receive elements R1, R2, . . . Rm are placed onthe surface of a body to be examined (such as a human or animal). Bothprobes can be sensitive to the same plane of scan, and the mechanicalposition of each element of each probe is known precisely relative to acommon reference such as one of the probes. In one embodiment, anultrasound image can be produced by insonifying the entire region to beimaged (e.g., a plane through the heart, organ, tumor, or other portionof the body) with a transmitting element (e.g., transmit element T_(x)1), and then “walking” down the elements on the Transmit probe (e.g.,T_(x) 2, T_(x)n) and insonifying the region to be imaged with each ofthe transmit elements. Individually, the images taken from each transmitelement may not be sufficient to provide a high resolution image, butthe combination of all the images can provide a high resolution image ofthe region to be imaged. Then, for a scanning point represented bycoordinates (i,j), it is a simple matter to calculate the total distance“a” from a particular transmit element T_(x)n to an element of tissue130 plus the distance “b” from the tissue 130 to a particular receiveelement. With this information, one could begin rendering a map ofscatter positions and amplitudes by tracing the echo amplitude to all ofthe points for the given locus.

Another multi-aperture system is shown FIG. 2 and consists of transducerelements in three apertures. In one concept, elements in the centeraperture 210 can be used for transmitting and then elements in the left220 and right 230 apertures can be used for receiving. Anotherpossibility is that elements in all three apertures can be used for bothtransmitting and receiving, although the compensation for speed of soundvariation would be more complicated under these conditions. Positioningelements or arrays around the tissue 240 to be imaged provides much moredata than simply having a single probe 210 over the top of the tissue.

The Multiple Aperture Ultrasonic Imaging methods described herein aredependent on a probe apparatus that allows the position of every elementto be known and reports those positions to any new apparatus the probebecomes attached. FIGS. 3 and 4 demonstrate how a single omni-probe 310or 410 can be attached to a main transducer (phased array or otherwise)so as to collect data, or conversely, to act as a transmitter where themain probe then becomes a receiver. In both of these embodiments theomni-probe is already aligned within the scan plan. Therefore, only thex and y positions 350 need be calculated and transmitted to theprocessor. It is also possible to construct a probe with the omni-probeout of the scan plane for better transverse focus.

An aspect of the omni-probe apparatus includes returning echoes from aseparate relatively non-directional receive transducer 310 and 410located away from the insonifying probe transmit transducer 320 and 420,and the non-directional receive transducer can be placed in a differentacoustic window from the insonifying probe. The omni-directional probecan be designed to be sensitive to a wide field of view for thispurpose.

The echoes detected at the omni-probe may be digitized and storedseparately. If the echoes detected at the omni-probe (310 in FIGS. 3 and410 in FIG. 4) are stored separately for every pulse from theinsonifying transducer, it is surprising to note that the entiretwo-dimensional image can be formed from the information received by theone omni. Additional copies of the image can be formed by additionalomni-directional probes collecting data from the same set of insonifyingpulses.

In FIG. 5, the entire probe, when assembled together, is used as anadd-on device. It is connected to both an add-on instrument or MAUIElectronics 580 and to any host ultrasound system 540. The center array510 can be used for transmit only. The outrigger arrays 520 and 530 canbe used for receive only and are illustrated here on top of the skinline 550. Reflected energy off of scatterer 570 can therefore only bereceived by the outrigger arrays 520 and 530. The angulation of theoutboard arrays 520 and 530 are illustrated as angles α₁ 560 or α₂ 565.These angles can be varied to achieve optimum beamforming for differentdepths or fields of view. α₁ and α₂ are often the same for outboardarrays, however, there is no requirement to do so. The MAUI Electronicscan analyze the angles and accommodate asymmetrical configurations. FIG.5A demonstrates the right transducer 510 being used to transmit, and theother transducer 520 is being used to receive.

FIG. 6 is much like FIG. 5, except the Multiple Aperture UltrasoundImaging System (MAUI Electronics) 640 used with the probe is astand-alone system with its own on-board transmitter (i.e., no hostultrasound system is used). This system may use any element on anytransducer 610, 620, or 630 for transmit or receive. The angulation ofthe outboard arrays 610 and 630 is illustrated as angle α 660. Thisangle can be varied to achieve optimum beamforming for different depthsor fields of view. The angle is often the same for outboard arrays;however, there is no requirement to do so. The MAUI Electronics willanalyze the angle and accommodate asymmetrical configurations.

In this illustration, transmitted energy is coming from an element orsmall group of elements in Aperture 2 620 and reflected off of scatterer670 to all other elements in all the apertures. Therefore, the totalwidth 690 of the received energy is extends from the outermost elementof Aperture 1 610 to the outmost element of Aperture 2 630. FIG. 6Ashows the right array 610 transmitting, and all three arrays 610, 620and 630 receiving. FIG. 6B shows elements on the left array 610transmitting, and elements on the right array 620 receiving. Using onetransducer for transmit only has advantages with regard to a lack ofdistortion due to variation in fat layer. In a standalone system,transmit and/or receive elements can be mixed in both or all threeapertures.

FIG. 6b is much like FIG. 5A, except the Multiple Aperture UltrasoundImaging System (MAUI Electronics) 640 used with the probe is astand-alone system with its own on-board transmitter. This system mayuse any element on any array 610 or 620 for transmit or receive as isshown in FIG. 6C. As shown in either FIG. 6B or FIG. 6C, a transmittingarray provides angle off from the target that adds to the collectiveaperture width 690 the same way two receive only transducers wouldcontribute.

Some embodiments described herein include a precision carrier for theproper alignment of a universal multiple aperture ultrasound transducer.Referring to FIGS. 7A-7C, transducer array 2161 can be already “potted”in its own fixture 2161 with lens 2162 intact. Potting procedures areconventional methods to secure the transducer array to its lens and tothe case. Flex circuitry, cabling, and attachment to the larger multipleaperture ultrasound transducer fixture can take place after the pottingprocedure is complete. A benefit of such embodiments is that they do notuse the same transducers during the alignment. Different transducerswith different “pots” can be utilized in any location of the alignmentfixture thanks to the flexibility of the alignment carrier.

FIGS. 8A-8C provide views of the basic structure and features ofembodiments of a precision carrier 2150 for a multiple apertureultrasound transducer array. FIG. 8A shows a top view of a precisionarray carrier 2150 with six positioning screws 2151. FIG. 8B shows aside view of a precision array carrier 2150 having two threaded screwholes 2180 on each side. When positioning screws 2151 are inserted intothreaded screw holes (e.g., screw holes 2155 and 2156 in FIG. 7B),adjustments may be made to employ longitudinal corrections 2159 to the“seated” array. FIG. 8C shows a side view of a precision carrier 2150with threaded screw holes 2180 located on each end. When positioningscrews are inserted into these threaded screw holes, adjustments may bemade to employ lateral corrections 2160 to the “seated” array (asillustrated in FIG. 7C).

FIGS. 9A-9D show a precision array carrier 2150 with an array-centeringgasket 2152 installed. FIG. 9A is a top view of the precision carrier2150, with an array-centering gasket 2152 placed at the bottom of thecarrier where the lens 2162 located in the center. FIGS. 9B-9D showside, end, and bottom views of the carrier, respectively. The arraycentering gasket 2152 can be located on the carrier's L-shaped shoulder2181, as illustrated in FIG. 9B. Further, as shown in FIG. 9B, thegasket 2152 can extend the entire length of the carrier over theL-shaped shoulder 2181. The gasket 2152 can extend around the corners ofthe L-shaped shoulder 2181 to cover the ends of the carrier as itillustrated in FIG. 9C. The gasket provides the array translationalcentering and a pivot point for positioning adjustments during operationwithout interfering with the integrity of the lens 2162. FIG. 9Dprovides a view of the lens 2162, the bottom of the precision carrierarray centering gasket 2152, and finally the L-shaped shoulder 2181.

Referring back to FIGS. 7A-7C, which show top, end, and side views,respectively of a precision array carrier 2150 with an array 2161inserted therein. The array 2161 is supported end-to-end by positioningscrews 2155 and 2156. The array can be supported from each side bypositioning screws 2153, 2154, 2157, 2158 and from the bottom by thearray centering gasket 2152. FIG. 7B shows the array 2161 in theprecision array carrier 2150 being supported by array centering gasket2152 and ready for longitudinal adjustment. Alternately tightening andloosening positioning screws 2155 and 2156 allows the array 2161 to beadjusted through arc 2159 to correct longitudinal axis errors. FIG. 7Cshows the array 2161 in the precision array carrier 2150 supported bythe array centering gasket 2152 ready for transverse alignment.Alternately adjusting positioning screw pairs 2157, 2158 and 2153, 2154allow the array 2161 to be corrected for transverse axis errors.

FIGS. 10A and 10B show a top views of a precision array carrier 2150with the array 2161 inserted. Arrows depict, respectively,counter-clockwise and clockwise rotational adjusting by way of selectivescrew adjustments. FIG. 10A shows a tightening of position screws 2153and 2158 while loosening position screws 2154 and 2157 shifting thearray 2161 in a counter-clockwise arc 2165 to correct rotational axiserrors. FIG. 10B shows a tightening position of screws 2154 and 2157while loosening position screws 2153 and 2158 to shift the array 2161 ina clockwise arc 2166 to correct rotational axis errors.

FIG. 11 shows an end view of a precision array carrier 2150 installed ona tissue equivalent phantom or test block 2182 and ready to transmit andreceive during alignment. A ‘phantom’ is a structure filled with tissueequivalent material that has a speed of sound characteristics similar tothat of human tissue with known voids and reflectors placed at knownlocations within the phantom. This end view of the phantom shows oneembodiment including three targets 2167 in profile view. These targetscan be echogenic, very reflective, or anechoic, void of reflection. Thetop target can be at a pre-determined depth D from the surface of thephantom and the face of array carrier 2150. The other targets can bespaced at distances D1 and D2 from the top target. In some embodiments,the pre-determined depth D can be 100 mm from the top target to the faceof the array. The other targets can have D1 and D2 distances of 10 mm,for example. However, any range of depths for the targets 2167 can beused, depending on the desired application of the transducer arrays. Theperpendicular targets 2167 serve to assist during the longitudinaladjustment of the array positioning. When correctly positioned, thethree targets would be displayed as exactly perpendicular to the frontof the array, and further, each target 2167 would be displayedequidistantly one a top the other.

FIG. 12 shows a side view of the phantom 2182 with the ends of thetargets 2167 visible. Once transmitting and receiving, a lateraladjustment could be made to the array 2163 in the carrier 2150. Thecorrect alignment is for achieved when all targets are visible above andbelow the center target 2168.

FIGS. 13A-13C show a precision array carrier 2150 with an array 2161inserted and aligned, in top, side, and end views, respectively. At thisstage an acoustic damping material 2162 can be poured into the gapbetween the array and the carrier to stabilize the position of arrays2161. FIG. 13B is a side view of the precision array carrier 2150showing the gap between the array 2161 and the precision array carrier2150 filled with acoustic damping material 2162. FIG. 13C shows the gapbetween the array 2161 and the precision array carrier 2150 filled withacoustic damping material 2162.

FIGS. 14A-14C show the precision array carrier 2150 with the array 2161inserted and aligned in top, side, and end views, respectively. Theacoustic damping material 2162 has cured and the six alignment screwshave been removed. FIG. 14B is a side view of the precision arraycarrier 2150 with the array 2161 inserted, aligned, the acoustic dampingmaterial 2162 cured and the position alignment screws removed: At thispoint, the precision array carrier 2150 with its captured array becomesa precision carrier array assembly 2163.

FIG. 15 shows a multi-aperture ultrasound probe assembly 2183constructed with precision transducer receptacles surrounded bystructural supports 2164. The structural supports 2164 can beconstructed out of many hard materials (e.g., metals or plastics) andusually are built into a larger structure such as the probe 2200 in FIG.22. In FIG. 15, the three precision carrier array assemblies 2163 areinserted into the precision transducer receptacles 2166.

FIG. 16 shows the multi-aperture probe assembly 2183 having precisiontransducer receptacles 2166 with the precision array assemblies 2163each locked into the receptacles, thus completing the construction ofthe multi-aperture ultrasound probe 2184 having three transducer arrays.

FIG. 22 shows a completed probe 2200 with arrays 1701, 1702, and 1703fitted in array receptacles and ready for submission to the calibrationcycle.

Alternative apparatus and methods for constructing and aligningmulti-aperture ultrasound probes will now be discussed. Variations inthe ultrasound beam displacement or rotation of both the insonifying andreceiving probes about the x, y and z axes are preferably detected andcorrected to achieve the best image quality. A MAUI alignment fixturefor aligning a multi-aperture probe uses one or more precision angularalignment controls, precision stage assemblies that provide for theadjustment, in 6 degrees of freedom of the each array under test.

One factor in making multi-aperture imaging systems is the importance ofprecisely aligning the elements of the multiple arrays. It is wellrecognized that by increasing the effective aperture of a probe systemby including more than one probe head and using the elements of all ofthe probes to render an image, the lateral resolution of the image canbe greatly improved. In order to render an image, the relative positionsof all of the elements are preferably known precisely. In someembodiments, if the probe system has position and rotation adjustments,a display is provided to position all of the elements to be in the sameplane of scan and to transmit or receive in the same plane of scan.

FIG. 17 shows a probe system 1700 comprising three probes 1701, 1702,and 1703 working together as a multi-aperture transducer though notassembled in a single shell. This is not a standard embodiment of amultiple aperture transducer, but serves here to aid in describingarrays alignment. A multi-aperture transducer can comprise of any numberof arrays 1710, 1720, 1730 (two or more), or even individual elements.For practical reasons, arrays in probes can easily be manufactured witha large number of elements and element spacing within a head can be wellcontrolled. If one can precisely position the end elements of eachprobe, it is possible to imply the positions of the other elements.Therefore, a fixture will be described which finds the positions of theelements. This apparatus could determine the exact location ofindependent elements either inside or outside of an array; however,because arrays are typically constructed in a linear format, theembodiment discussed here only identifies the end elements.

In FIG. 17 these end elements are designated as element numbers 0through 5, where 0 and 1 are the end elements of array 1710, 2 and 3 arethe end elements of arrays 1720 and 4 and 5 are the end elements ofarray 1730. Any of the intermediate elements could be located in thesame way as will be described.

A precision alignment stage assembly is shown in FIG. 18A. The far leftarea of the assembly 1801 allows for the mechanical connection of asingle probe, such as 1701 from FIG. 17. The precision alignment stageassembly has three separate mechanisms 1801, 1802 and 1803 that controlthe position of the attached array in x, y and z axes. Several alignmentstage assemblies can be used in concert so that multiple probe arrayscan be manipulated independently. FIG. 18B allows the operator tomanipulate an array in any axis by using controls 1805, 1806, 1807,1808, and bearing 1809. Precision screws 1804, 1805, 1806, 1807, and1808 can be adjusted, and bearing 1809 can be rotated to affect one ormore axes for the array during the alignment process.

FIG. 25 shows the arrays 1710, 1720 and 1730 attached in line toprecision alignment stages 2510, 2520 and 2530. With the arrays set inplace, they can now transmit to common points of interest and comparetheir points of impact with the other arrays.

As used herein, calibration of an ultrasound probe may involvedetermining the acoustic position of each individual ultrasound elementin a probe with a desired degree of precision relative to some knowncoordinate system. The basic technique for aligning and calibrating amultiple aperture probe can be seen with reference to FIGS. 19A, 19 and20.

FIG. 20 illustrates probes 1701, 1702 and 1703 from FIG. 17 now attachedto alignment stage assemblies above a tank or test block 2012. The tankcan be filled with any liquid, fluid, gel, solid, or other medium 2014that is desirable for manufacture and safety considerations, as long asthe speed of sound for the fluid is known. The tank can include amounting location for the alignment stage assemblies. In someembodiments, as shown in FIG. 20, multiple alignment stage assembliesholding transducer elements can be mounted on the test block. From thisposition, it is possible to transmit ultrasonic pulses from the elementsof any of the arrays to be received by ultrasonic sensor or hydrophones2085 at the other end of the tank 2012.

As used herein, the term “hydrophone” is used in a generic sense andrefers to any instrument capable of accurately receiving and transducingultrasound waves into electronic signals. In some embodiments,hydrophones may also be used to transmit ultrasound signals. Thus, insome embodiments, hydrophones may comprise piezoelectric transducerarrays, or any other suitable technology. The term “hydrophone” isgenerally used herein to refer to ultrasound receiving and/ortransmitting instruments attached to a calibration system, as distinctfrom the transducer elements and arrays of ultrasound imaging probes tobe calibrated.

As shown in FIGS. 19A-19B, the hydrophone 2085 can be a multi-axisultrasonic hydrophone 2085 configured to detect the X, Y and Z positionsof each element of a single array or multiple arrays under test. Themulti-axis hydrophone 2085 can include a transverse hydrophone 2086, andright and left hydrophones 2087 and 2088. The common targets for theprobes 1701, 1702 and 1703 to shoot at are elements 2091, 2092 and 2093on the right hydrophone 2087. On the left hydrophone 2088, elements2094, 2095, and 2096 are the targets.

In use, the probe can be attached to a signal generator configured toexcite any of the transducer elements to transmit ultrasonic pulses. Anultrasonic signal is transmitted which exhibits good autocorrelationproperties (e.g., a long frequency sweep, or ‘chirp’ waveform, a short(wideband) pulse, a spread spectrum waveform, etc) from at least oneelement in arrays 1710, 1720 and 1730. The transmitted ultrasound signalcan travel through the test block and be received by the receivinghydrophone transducer elements 2091, 2092, 2093, 2094, 2095, 2096 andthe transverse hydrophone 2086. It is important to note that detectionof the ultrasonic signal or pulse as received by the hydrophone arrayscannot be detected accurately enough by cross correlation with thesignal impressed on the probe element because the probe element itselfdistorts the signal.

Two innovative techniques are used to obtain the needed accuracy infinding the relative time delays and hence the relative distances. Thefirst technique is to use cross correlation between the signal receivedat one element of the hydrophone (for example 2091) and the signalreceived at another element of the same hydrophone (for example 2093).The correlation peak will yield the time difference and thus thedistance difference.

The second technique is to interpolate between samples of the receivedwaveforms to obtain better time resolution than simply the samplinginterval. Perhaps the best way to accomplish both of these tasks is totake the Fourier transform of both signals, fill in zeros for the highfrequency components of a much larger transform. Call these largertransforms FFT 1 and FFT 2. Then find the peak of the inverse transformof (FFT 1*(conjugate of FFT 2)).

A third technique may be used to convert differential distances to totaldistance. Consider the triangle bce in FIG. 21A where the point brepresents one of the elements for which we need to compute a position,and c and e are known reference points in the bottom of the water tank.The distance d₄ represents a total distance between the test element atpoint b and the hydrophone element at point c (840 or 870). Similarly,the distance d₀ represents a total distance between the test element atpoint b and the hydrophone element at point e (820 or 850). It isdesired to measure the lengths d₄ and d₀ by triangulation, but justknowing the difference between d₀ and d₄ is not enough. By adding atransverse hydrophone (see 2086 In FIG. 19A) in the bottom of the tankwe have two triangles from which we can compute d₀ and d₄. Let e, d, andc be the locations of the hydrophones 2094, 2095 and 2096 or 2091, 2092and 2093 of FIG. 19A.

For the following analysis, the hydrophones 2094, 2095 and 2096 arepreferably on the same line and on a parallel line to that formed by2091, 2092 and 2093. The distance between 2094 and 2095 is designated dand the distance between 2095 and 2096 is designated d₃. d₁ and d₃ arepreferably known precisely as this becomes the reference “yardstick” forthe other measurements. 2095 should be roughly centered between 2094 and2096 LN, but d does not need to equal d₃. The same is true for R0, RC,and RN.

Let d 2 be the reference distance and define measured distances as:

d ₂ m=d ₂ −d ₂=0

d ₀ m=d ₀ −d ₂

d ₄ m d ₄ −d ₂

From the law of cosines we have

d ₄ ² =d ₂ ² +d ₃ ²−2d ₃ d ₂ cos α

d ₀ ² =d ₂ ² +d ₁ ²−2d ₁ d ₂ cos(π−α)=d ₂ ² +d ₁ ²+2d ₁ d ₂ cos α

cos α=(d ₄ ² −d ₂ ² −d ₃ ²)/(−2d ₃ d ₂)=(d ₀ ² −d ₂ ² −d ₁ ²)/(2d ₁ d ₂)

d ₄ ² −d ₂ ² −d ₃ ²=−(d ₀ ² −d ₂ ² −d ₁ ²)d ₃ /d ₁

(d ₄ m+d ₂)² −d ₂ ² −d ₃ ²+(d ₀ m+d ₂)² d ₃ /d ₁ −d ₂ ² d ₃ /d ₁ d ₃=0

Combining and canceling terms this becomes

d ₂=(−d ₄ m ² +d ₃ ² −d _(om) ² d ₃ /d ₁ +d ₁ d ₃)/(2d ₄ m+2d ₀ md ₃ /d₁)

Then d₀=d_(0m)+d₂ and d₄=d_(4m)+d₂.

Thus we have the full measurements from received differential times.

Two parallel “yardsticks” or right and left hydrophones are provided inthe bottom of the tank in order to measure position along the z axis(i.e., the axis perpendicular to the scan plane), as illustrated in FIG.23B. It will be the goal to position all of the probe elements from allthree arrays 1701, 1702 and 1703 in a line midway between the twoyardsticks using the various controls illustrated in FIG. 18B.

Referring now to FIG. 21B, consider the measurement of the position ofany probe element such as M0 1206. First, consider using the rightyardstick R 0-RC-RN 2091, 2092, 2093. By transmitting a chirp signalfrom element M0 1206 and receiving it on hydrophones at R0, RC, and RN2091, 2092 and 2093, one can calculate the differential times fortransmission along the paths d₀, d₂, and d₄. Times can be converted todistances if the speed of ultrasound of the test block medium is known.If the test block medium is water, the speed of sound is approximately

sos=1.40238742+5.03821344*TE/1000.−5.80539349*TÊ2/100000.+3.32000870*TÊ3/10000000.−1.44537900*TÊ4/1000000000.+2.99402365*TÊ5/1000000000000in mm per microsecond where TE is the temperature in degrees Celsius.Differential distances can be converted to total distances according tothe derivation above.

Now from trigonometry, distance a=(d₀ ²−d₄ ²+(d₁+d₃)²)/(2(d₁+d₃))

The position along the x′ axis is d₁−a.

Assuming that the element is midway between the two yardsticks, then theposition along the y′ axis is sqrt((d₀ 2−a²−(zr/2)²)).

Initially considerable error may occur as a result of this assumption,but the measurement of z will allow for adjustment of the element or theentire probe assembly until this assumption is satisfied.

Again referring to FIG. 21B, the same computations for x′ and y′ can bemade using the left hydrophone array 2094, 2095 and 2095. In someembodiments, the results of the measurements made with the righthydrophone array may be averaged with results of measurements made withthe left hydrophone array.

Advantageously, by having two hydrophone arrays or “yardsticks,” the zaxis can be measured, i.e., the position of the elements in or out ofthe scan plane. Then the array alignment apparatus can display it (seeFIG. 22A, 2300), and thus allow either manual (FIG. 18B) or automatic(FIG. 24) correction and alignment. The z variable is related to thetime of arrival difference of the pulse as received at RC 2092 and LC2095. The probe position should be adjusted until the time difference isclose to zero. When this is done, all of the x and y measurements willbe accurate and the relative positions of all of the elements will beknown.

In some embodiments, the right and left hydrophone arrays may be used tomeasure an acoustic position of a test element along the z axis; i.e.,the test element's position in or out of the scan plane. In someembodiments, following such a measurement the calibration system maydisplay and/or automatically correct an alignment of the probe withinthe docking area of the calibration system. In other embodiments, thecalibration system may direct an operator to manually adjust analignment of the probe.

The z variable may be proportional to the distance d2 as computed fromthe hydrophones on track 845 minus the distance d2 as computed from thehydrophones on track 875 in FIG. 34A. In some embodiments, the probeposition may be adjusted until this difference is close to zero.

In other embodiments in which the probe element cannot be mechanicallycentered between the two tracks, the z position can be computed. This isparticularly true for 1.5D probes and 2D probes where it is not possibleto position all elements simultaneously to a central position. In thesecases, the acoustic position of elements along the z axis may be storedin the calibration table along with x and y coordinates as discussedabove.

The value of z can be computed through a straightforward trigonometriccalculation as illustrated in FIG. 21C.

Let m=the distance d2 as computed from the hydrophones on track 845 andlet n=the distance d2 as computed from the hydrophones on track 875.

Let w indicate half the known distance between the two tracks.

n2=(w−z)2+y2

m2=(w+z)2+y2

then n2=(w−z)2+m2−(w+z)2

and z=(m2−n2)/4w.

In some embodiments, the transverse hydrophone array may be used todetermine an angular displacement of a probe test element. In someembodiments, such information may be used to direct automatic or manualre-positioning of the probe. In alternative embodiments, suchinformation may be incorporated into stored calibration data.

In some embodiments, a controller, such as a computer, can scan and findthe maximum signal strength on the transverse hydrophone 2086 and recordthe angular displacement for the probe element.

To use the multiple aperture array alignment apparatus as a dailycalibrator, multiple aperture ultrasound transducers may already befully assembled, such as the embodiment illustrated in FIG. 22.Therefore, all of these measurements will preferably be referenced toaxes on the probe assembly. In the multi-aperture transducer probeassembly 2200 shown in FIG. 22, it would be reasonable to rotate andtranslate all measurements to a new coordinate system (x,y) centered onthe center array. The appropriate coordinate system would be dependenton the ultrasound imaging system for which the probe assembly would beused. The multi-aperture probe can have a resident calibration memory orcal chip 2201 that can be programmed with calibration data received fromthe automated precision stage assembly, described below.

The transmit synchronization module 2202 is not related to calibration,but may be used to identify the start of pulse when the probe is used asan add-on device with a host machine transmitting. The probedisplacement sensor 2203 can be an accelerometer or gyroscope thatsenses the three dimensional movement of the probe. During calibration,the probe should be securely attached to the array alignment apparatusso that the probe is still. The calibration system may then compareinformation from the position sensor of the probe with information fromthe position sensor of the calibration tank 122 to determine whether theprobe is properly aligned.

Referring now to FIG. 23A, a proprietary graphical user interface or GUI2300, allows the elemental array data to be visualized in real-timeallowing for correction of the x, y and z variation errors. The two widevertical lines 2001 and 2003 represent the z positions of the yardsticksR 0-RC-RN (2091, 2092, and 2093 from FIG. 19A) and L 0-LC-LN (2094,2095, and 2096 from FIG. 19A). The thinner vertical line 2302 is the z=0line and the desired position of each of the elements of a probe system.The vertical position is the x coordinate.

Each small square, such as 2305, 2306, 2307, 2308, 2309, 2310 and 2011,is the position of a probe element in the x-z plane. In this examplethere are six small squares indicating the positions of the end elementsof three probe heads. However, the positions of more or fewer elementscould be displayed in this way. The thin horizontal lines 2312, 2313,2314, 2315, 2316, 2317 and 2018 represent the directivity and angularspread of each element as detected on the multi-axis hydrophone. Auseful angular spread measure is the number of hydrophone elements onthe transverse hydrophone array which record signal strength greater orequal to half of the maximum strength.

FIG. 23B depicts a probe element positioned correctly with the zposition 2305 at or near z=0 and its directivity positioned over thecenterline. In contrast, FIG. 23C depicts a probe element with its zposition 2305 offset toward the right hydrophone. The resulting displayshows the small square, 2305, to the right of centerline, 2302. Notethat in this case, the element position is in error, but the elementdirectivity remains over the centerline as indicated on the display bythe horizontal line 2312 remaining centered over centerline, 2302.

Finally, FIG. 23D depicts a probe element correctly positioned with itsz 2305 position at or near z=0, 2302. The directivity 2312, however, ismisaligned in this case with an offset toward the left hydrophone asindicated by the horizontal line shifted to the left of centerline,2302. In this case, the directivity needs to be corrected by adjustingthe angulation to bring the directivity back over center. This could beaccomplished, for example, by using controls 1805 and 1807 in FIG. 18B.Thus with this display, element position and directivity can bemonitored simultaneously and both brought into alignment.

Adjustments of the probe position and angulation with the precisionalignment stage assembly or assemblies should continue until all of thesmall squares and all of the horizontal lines arc aligned on the centervertical line as closely as practicable, ensuring in alignment in the zaxis. As this is done, the x and y positions will be computed accuratelyand no separate iteration will be required for these.

In some manufacturing formats, arrays 2406 could be loaded into anautomated precision stage assembly like the one in FIG. 24. Here, arrayswhile still within their nose pieces can still be manipulated. In FIG.24, we see an automated precision stage assembly, 2406, fitted withprecision stepper motors, 2403. Stepper motor controller, 2401, drivesthe transducer, 2405, under test in response to instructions fromcontroller, 2402. The controller, 2401, evaluates data from thehydrophone assembly, 2404, and calculates transducer corrections. Testprograms residing in the controller, 2402, provide transducer specificcalibration data back to the transducer, 2405, under test incorporationin its on board calibration chip, 2201. This automatically acquiredelement and array position data would be MAUI probe specific and wouldbe used to optimize probe and system performance.

Using the precision stage assemblies with the array alignment system isonly part of the value of the system. FIGS. 20A and 20B illustrate arrayalignment systems 2610 attached to the control unit 2620 of anultrasound machine 2600. A cut away shows hydrophone assembly 2085 islocated at the bottom of the fluid filled system 2610. In FIG. 26A aMAUI general radiology probe 2630 is affixed to the system for testing.In FIG. 26B, a MAUI cardiac probe 2640 is affixed to the system forcalibration. The portability of this system, therefore allows forcalibration of probes in the field multiple times per day. Additionallythe MAUI system would alert the operator if service or maintenance wasrequired.

To calibrate a probe, MAUI electronic apparatus can send a test patternto the arrays in the probe to transmit to the hydrophone assembly 2085.When the positions of the probes and their directivities are reported asa result of the sequence, the positions of all of the elements can bedownloaded to a file specific to that probe. Each file may be stored inthe probe calibration chip 2201. The calibration chip may report elementpositions in x, y and z axes to every MAUI electronic apparatus itconnects to, and therefore can perform multiple aperture imaging withoutrecalibrating before use with a different MAUI apparatus. Thecalibration chip memory can also be used to analyze probe performanceand reliability.

In the special case in which all of the transmit and receive elementsare aligned in the same plane or are manufactured so that there is noadjustment in z position, a simplified alignment fixture can be used.Instead of two parallel “yardsticks” of hydrophones, a single yardstickcan be used. In this case the probe would be centered over the singleyardstick using a plumb bob or a clamping device. The x and ymeasurements would then be made assuming z=0 and zr=0. This is possiblesince accuracy in the value of z is much less critical in beamformingthan is accuracy in the values of x and y. Thus adjusting z by therelatively crude methods of sighting with a plumb bob or clamping to amachined edge of the probe can be acceptable in spite of the highaccuracy demands for measurement of x and y. Obviously, the cost of thissimplified fixture would be much reduced resulting in a fixture whichcould be used in the field rather just in the probe assembly factory.

Embodiments below provide further systems and methods for calibratingultrasound imaging probes as well as systems and methods for testingquality assurance characteristics of ultrasound imaging probes. Althoughthe following embodiments are shown and described with reference tomultiple aperture ultrasound imaging (MAUI) probes, the skilled artisanwill recognize that many features of the systems and methods describedmay also be applied to ultrasound probes of any configuration where itis desirable to determine the acoustic position or the health of one ormore ultrasound transducer elements in an ultrasound probe.

As discussed above and with further reference to FIGS. 28, 34A, and 34B,some embodiments of a calibration process may comprise three stages:First, a single test-element of the probe may transmit an ultrasoundtest signal into the calibration tank 122 through the filler material210. Second, the hydrophones 230 may receive the ultrasound test signal,and associated electronics and/or software may geometrically triangulatethe origin of the test signal in order to determine an acoustic positionof the test element to within a desired degree of accuracy. Third, theacoustic position of the test element may be transformed into acoordinate system with a known origin relative to the probe. Coordinatesfor the test element may be stored in a table of coordinates associatedwith the probe. These steps may then be repeated for each transducerelement in each transducer array within a probe until the acousticposition of each element is determined and recorded in a table ofcoordinates.

Embodiments of the systems and methods herein may quantify bothtransmitted and received ultrasonic pulses and use the informationobtained to identify the acoustic position of single transducer elementsand/or full arrays of transducer elements. Further, embodiments of thesystems and methods herein may also quantify the “health” of probeelements. The “health” of a probe element may refer to a number offactors including transmitting and receiving efficiency of probeelements, element sensitivity, and electronic functionality.

Probes with multiple aperture arrays may be properly aligned duringproduction as discussed above. However, regularly recalibrating anultrasound probe throughout the life of the probe as opposed to onlyduring manufacturing can allow for high quality imaging over a longperiod of time without requiring the probe to be returned to amanufacturer or repair facility. To address these needs, a calibrationsystem may be provided to accompany probes into the field. In someembodiments, a calibration system may be attached to or integrallyformed with an ultrasound control panel. In some embodiments, acalibration system may include a tank in the shape of an open-topped boxwith a mounting portion in a top section of the box for holding a probein a calibration orientation and a plurality of receivers at a bottom ofthe box for receiving ultrasound signals transmitted from the probe.

By providing a calibration system as an attachment to an ultrasoundimaging system, the calibration system becomes easily accessible tooperators. In some embodiments, the calibration system may serve as aprobe storage location for holding probes not in use. In someembodiments, a plurality of imaging probes of different configurationsmay be stored in the calibration system. Probes may then be selectivelycalibrated according to a calibration process, thus making a wide rangeof probe designs readily available for imaging. Moreover, adjustablemultiple aperture probes may be re-configured into a different shape andthen recalibrated for each patient.

Referring to FIG. 27A, a calibration system 120 may work in conjunctionwith a control panel 100. The control panel 100 can contain and controlelectronic hardware and software configured to transmit, receive andprocess ultrasound signals using a multiple aperture ultrasound imaging(MAUI) probe. Such hardware and software is generically referred toherein as MAUI electronics. As shown in FIG. 27A, the calibration system120 may be externally mounted to a control panel 100. In suchembodiments, the system 120 may be electronically connected to the MAUIelectronics by a wired system which may include any desired wiringarrangement, such as wiring harnesses or removable plugs. Alternatively,referring to FIG. 27B, a calibration system 120 may be embedded into thecontrol panel 100. In further embodiments, a calibration system 120 maybe provided as an entirely separate device, which may be electronicallyconnected to the MAUI electronics by any suitable wired or wirelessarrangement. In further embodiments, the electronics controlling acalibration system, including electronics controlling a probe duringcalibration may be entirely independent (physically and/orelectronically) of the electronics used for controlling an ultrasoundimaging process.

As shown in FIG. 28, in some embodiments the calibration system 120 mayresemble a rectangular tank that may be relatively small in size withoutthe bulky alignment features that can be required during manufacturing.In some embodiments, an opening at the top of the tank 122 may be sizedto receive a probe 370. The tank 122 may have an overall heightapproximately the length of a pencil box (e.g., between about 10 and 24inches in some embodiments), although larger or smaller tanks may alsobe used. In some embodiments, a width and/or depth (e.g., in/out of theplane of FIG. 28) of the tank 122 may be sized to minimize un-desiredreflections from side walls of the tank. Additionally, a material andinternal surface texture of the tank 122 may also be engineered tominimize noise from undesired reflected ultrasound waves.

In some embodiments, a matrix of ultrasonic sensors or hydrophones 230may be attached to the bottom of the tank 122. The matrix of hydrophones230 can function similar to the multi-axis hydrophone 2085 describedabove. It is desirable for the calibration tank 122 to be configuredsuch that an entire ultrasound path between the probe and all receiversis occupied by a material with a consistent and known speed of sound.Thus, similar to the tank 2012 described above, the tank 122 may befilled by a filler 210 made of a liquid, gel or solid material with aconsistent and known speed of sound. The filler 210 may be any materialthat is desirable for manufacture and safety considerations. The speedof sound through the filler 210 should be known precisely in order toaccurately calculate the distance traveled by any given ultrasound pulseduring a calibration process. In one embodiment, the filler 210 is madeof a relatively rigid ballistics gel. The filler 210 can occupysubstantially all of the tank 122. In some embodiments, the filleroccupies most of the tank 122 except for a top layer which may bereserved for a docking area 220 configured for receiving an ultrasoundprobe to be calibrated.

In some embodiments, the docking area 220 may be an empty void which maybe filled with a liquid or gel which may conform to a shape of a probeto be calibrated such as the illustrated multiple aperture probe 370. Inother embodiments, the docking area 220 may include a molded piece ofballistics gel (or other suitable material) configured to conform to theshape of a probe to be calibrated. Preferably, the material used in thedocking area 220 has substantially the same speed of sound as the fillermaterial 210. In other embodiments, the docking area and/or the entirefiller may comprise a flexible bladder filled with a suitable liquid orgel material. In some embodiments, the probe and/or the docking area maybe coated with an ultrasound coupling gel as will be clear to theskilled artisan.

For the best results, probes should be substantially immobile during allcalibration and quality testing. To reduce error the calibration system120 may be equipped with a mechanical docking device configured to holdthe probe(s) in a substantially rigid and consistent position. Referringto FIG. 31, in some embodiments, an adjustable clasp 510 may be providedto capture and hold a probe 370 by a handle section or any othersuitable portion of the probe. In other embodiments, a clasp or graspingelement may be integrally formed with the docking area 220. In someembodiments, the docking area 220 and/or a clasp 510 may includeelectronic contacts or other elements which may interact withcorresponding features on a probe to ensure consistently properpositioning of the probe for calibration.

In other embodiments, accelerometers, gyroscopes or other positionsensors within the probe may be used to inform an operator of proper orimproper positioning of a probe within a docking area of a calibrationsystem. In some embodiments, corresponding position sensors (e.g.,gyroscopes, accelerometers or other sensors) may be provided in or onthe calibration tank. A calibration system may then compare informationfrom the position sensor of the probe with information from the positionsensor of the calibration tank 120 to determine whether the probe isproperly aligned for calibration.

FIGS. 32A-33B illustrate embodiments of docking devices 610 that may beused in a docking area of a calibration system. FIG. 32A shows anembodiment of a docking device 610 with a plurality of probe-specificmolded receivers (602-628). In such an embodiment, each probe that mightbe used with a particular system may have a specific receiver within thecalibration system. For example, the top center docking site 604 may beconfigured to receive a curvilinear MAUI probe 375 having a continuousconcave curved array 378 of ultrasound transducer elements such as thatshown in FIG. 29B.

FIG. 32B is a cross-sectional view of the calibration tank taken throughline A1-A in the plan view of FIG. 32A. In some embodiments, eachdocking device molded receiver may be manufactured to best fit thespecific needs of each probe; this can be especially useful for probeswith a more tight curvature or uniquely designed probes.

Other embodiments, as shown for example in FIGS. 33A and 33B may featureinterchangeable docking receivers custom made for each transducer. Thedocking receivers 710, 720, and 730 may be removably attached to adocking area 220 of the calibration system. Each receiver 710, 720, and730 may be formed for a specific type of probe. In further embodiments,one or more receivers may be configured to receive any of the probesshown and described in U.S. patent application Ser. No. 13/029,907 nowpublished as US Patent Publication 2011/0201933, and incorporated hereinby reference.

In some embodiments, the dock may be configured such that the ultrasoundprobe may be stored in the dock when not in use. The user or operatorcan then optionally calibrate the probe prior to removing the probe fromthe dock.

In some embodiments, one or more temperature sensors may be provided andconfigured to measure a temperature of the filler 210. As discussedabove, the temperature of the filler material 210 is used to calculatethe acoustic position of transducer elements in a probe duringcalibration. Thus, in some embodiments, a plurality of temperaturesensors (e.g., thermocouples, thermistors, optical thermal imagingsystems, etc.) may be positioned throughout the tank to obtain enoughmeasurements to determine an average temperature of the filler 210 atany given time. In other embodiments, a single temperature sensor may besufficient.

In some embodiments, a hydrophone matrix 230 such as that shown in FIG.34A and FIG. 28B may be used to detect the X, Y and Z positions of eachelement of a single array or multiple arrays in a probe undercalibration. In some embodiments, the multi-axis hydrophone 230 caninclude a transverse hydrophone array 810, a right hydrophone array 845and a left hydrophone array 875. In other embodiments, the hydrophonematrix may include only a single array of hydrophone elements. In otherembodiments, a hydrophone matrix may comprise a two-dimensional array ofmany detector elements to enable further measurements. For example, thehydrophone matrix may comprise a 3×3 array, a 4×4 array, a 4×6 array orany other ‘n’×‘m’ array of hydrophone elements.

In some embodiments, the hydrophone matrix 230 may act as a target whenthe probe is firing. In some embodiments, hydrophone elements selectedto be detectors to may depend on the size, shape and orientation of theprobe to be calibrated. In some embodiments, such calibration processdetails may be stored in the calibration chip or another data store incommunication with the calibration system electronics.

Ultrasound transducer elements or arrays of elements are typically cutfrom a common crystal wafer (e.g., of a piezoelectric crystal) to form1D, 1.5D and 2D arrays. Alternatively, some ultrasound elements may beprinted or machined into a micromachined lattice structure to form anarray called a Capacitive Micromachined Ultrasonic Transducer (CMUT)array. FIG. 24A illustrates a 1D piezoelectric transducer array in whicheach rectangular segment represents a single transducer element 400.Such an array is referred to as one-dimensional because the array hasonly rows of longitudinal transducer elements without columns. FIG. 24Billustrates a 2D piezoelectric transducer array in which each squaresegment represents a separate transducer element 400. Such an array isreferred to as 2-dimensional because the array of elements extends intwo directions, having both rows and columns. FIG. 30C illustrates aCMUT array in which each transducer element 400 has a more complexgeometric shape. Furthermore, a CMUT array has a much more complexarrangement, where elements are not necessarily arranged in rows andcolumns.

In the case of conventional 1D and 1.5D phased array probes, theposition of the elements is often roughly determined by the size of thecuts inside the crystal wafer upon initial manufacture. Referring toFIG. 30B, in this process, the acoustic center of each element isassumed to be at the center of the shaped crystalline structure 440,usually a parabolic channel running down the mid portion 420 of theelements. This may or may not be the true acoustic center of the elementdue to slight variations in the structure of the PZT crystal orvariability in the machining process. Nonetheless, transmit and receivebeamformers typically assume that the acoustic center position of atransducer element is coincident with its geometric center. When thetrue acoustic center of an element is not exactly at the geometriccenter (e.g., along the longitudinal axis 420), then both transmitwaveform energy and echoes being received are not being optimized. Theyare subject to the errors of being out of alignment, which detrimentallyaffects image quality and depth. The same problem may also exist for1.5D, 2D and CMUT arrays. Therefore, even traditional single-aperturephased array probes may benefit from regular calibration using thesystems and methods described herein.

Once an ultrasound probe is firmly mounted in the docking area of thecalibration system, a calibration process may be initiated. In someembodiments, a calibration process may be initiated by a user pressing abutton (e.g., 140 in FIG. 27B) on a calibrator or imaging system controlpanel.

In some embodiments, the calibration system may be configured todetermine the acoustic position of transducer elements relative to asingle array of which an individual test element is a part. For example,in the case of a multiple aperture probe such as that shown in FIG. 29A,the acoustic position of each element on the center array 350 maybedetermined relative to a coordinate system 380 centered on that array.Similarly, the acoustic positions of elements in the left 340 and right360 arrays may also be determined relative to separate coordinatesystems centered on those respective arrays.

A further calibration process may then be employed to detect theposition of one full array relative to another, thereby providinginformation describing the relative positions of the three coordinatesystems. In such an embodiment, test signals may be transmitted fromelements at opposite ends or corners of each array to be locatedrelative to other arrays. This may allow for the measurement of thelength, acoustic center and 3-dimensional orientation of each arrayrelative to other arrays in a probe containing multiple arrays. Forexample, the position and orientation of a planar transducer array maybe determined by identifying the three-dimensional location of asufficient number of array elements to define the orientation of thearray's planar surface. In some embodiments, three elements may besufficient to define the plane of an array. In other embodiments,several or all elements may be located to define the orientation of thearray's plane. In some embodiments, information describing theorientation of a planar array may be stored along with other calibrationdata. Such embodiments may be especially useful when calibratingadjustable probes which may contain two or more physically separatearrays which are free to move relative to one another.

In some embodiments, the calibration system can be configured totransmit a new test signal to the hydrophone matrix from every elementof the probe such that the acoustic location of every element of theprobe can be determined. In other embodiments, a test signal can be sentfrom only a few of the probe elements, such as two probe elements in anarray, and the remaining locations can be determined throughinterpolation.

Many transmit pulse patterns may be used in the step of transmitting anultrasound test signal from a test element. In some embodiments, anultrasonic test signal may be transmitted which exhibits goodautocorrelation properties. In some embodiments, such a test signal maycomprise a long frequency sweep, a ‘chirp’ waveform, a spread spectrumwaveform, a ‘ping’, a pseudorandom sequence, or another suitablepattern. In some embodiments, a test signal may be selected to requireminimal computational complexity.

As will be clear to the skilled artisan in view of the discussionherein, the only directly measurable ultrasound parameter in thecalibration system is the time delay between transmission of a testsignal from a probe test element and receipt of the test signal at eachhydrophone element. Based on these time delays, known speed of soundthrough the filler material, and known physical geometry of thecalibration system, the position of a test element may be calculated.

It is important to note that in many cases, a test element may distortthe timing of a transmitted signal. Thus, in some embodiments, it may bedesirable to perform time delay measurements without relying on apresumed “transmit time” as determined by a time of sending anelectrical signal to a transducer element. In such embodiments, thetotal distance traveled by an ultrasound test signal may be determinedby using only the speed of sound and the difference between the time atwhich the test signal is received at a first hydrophone element and atime-of-receipt of the test signal at a second hydrophone element.

Multiple techniques, such as those described above with reference toFIGS. 21A, 21B & 21C, may be used to obtain the needed accuracy infinding the relative time delays and hence the relative distances,including using cross correlation between the signal received at onehydrophone element (e.g., 820) and the signal received at anotherelement of the same hydrophone array (e.g., 840), interpolating betweensamples of the received waveforms to obtain better time resolution thansimply the sampling interval, and converting a differential distancemeasured by two hydrophone elements to a total distance traveled by anultrasound test signal.

Referring to FIG. 28, a coordinate system 260 can be establishedrelative to the hydrophone matrix. In FIG. 28, the X-axis is alignedwith left and right directions in the tank, the Y-axis is aligned withthe “up and down” directions in the tank, and the Z-axis isperpendicular to the scan-plane and the plane of FIG. 28. The positionof a plurality of probe elements, such as every probe element, can thenbe determined relative to the coordinate system 260.

In some embodiments, position measurements may be translated from thecoordinate system 260 with an origin relative to the hydrophones matrixto a coordinate system 380 with an origin located on the probe itself,as shown in FIG. 29. In the coordinate system 380 shown in FIG. 29, theX-axis lies along a center line of all three arrays, the Y-axis isperpendicular to the plane of the center array, and the Z-axis isperpendicular to the X & Y axes, extending in and out of the page ofFIG. 29A. In some embodiments, a process of rotating and translatingcoordinates may be used to translate the coordinate systems. In someembodiments, an appropriate probe-relative coordinate system may bedependent on the ultrasound imaging system for which the probe assemblyis to be used.

With a conventional array, a transmit pulse from a transmitting elementto a reflector is easily calculated back to a given receive element.Assuming a constant speed of sound, the positions in a conventionalmatrix or linear array are mechanically assumed so that transmit andreceive paths can be easily computed. In multiple aperture imaging it isimportant to determine the position of each element relative to theposition of any other element(s) in a known space such as a Cartesian X,Y, and Z coordinate system illustrated in FIG. 31 for example. In someembodiments, such a coordinate system may have one element designated asan origin and acoustic center positions of all other element(s) may beassigned coordinates relative to this initial position. From this theposition of any element may then be known relative to any other.

As will be clear to the skilled artisan, the origin of a coordinatesystem may be centered at any element, or at any other point on or offof the probe. Additionally, the calibration system need not necessarilyuse a Cartesian coordinate system; any suitable coordinate system may beused, provided that such a coordinate system gives accurate informationabout the position of transducer elements.

The information obtained through calibration as well as the newcoordinate system may then be compared to original element positioninformation for the probe, as well as any previous calibration data. Insome embodiments, this information may be tracked over time to betterunderstand the properties of the probe elements and the probes as theyare used. In some embodiments, this time-series calibration informationmay be stored and/or analyzed in an ultrasound imaging system, a remoteserver system, or any other suitable computing system.

During manufacturing, each MAUI transducer may be properly aligned andcalibrated according to the type of crystal matrix used. The initialcoordinate system and calibration may then be programmed into a memorychip 310, which can be set in the handle of the probe as shown in FIG.29A. When the probe is recalibrated at some later time, the calibrationsystem electronics may compare the new calibration results to theinitial or last-known position of the elements. Difference data or newposition data may then be updated in the calibration chip 310. Besidesmaintaining the calibration data, calibration chip 310 may also containdata for setting up a general layout of each probe, this information maybe used to inform the calibration system of the number of elements tofire and in roughly what order or design during calibration.

In some embodiments, calibration data for a probe may be stored in alocation other than the probe itself. It is generally desirable forcalibration data to be associated specifically with the probe itdescribes, but such information may be stored in any practical physicallocation. For example, in some embodiments, a probe may have an ID chipwhich carries substantially only an identification number which may beused to retrieve a unique calibration record stored in a remote (e.g.,internet-accessible) database, in an ultrasound imaging system, or anyother location. In some embodiments, communications systems may also beprovided to allow for logging of calibration data into an ultrasoundimaging system data log, and/or sending to a service provider and/orproviding an operator with an appropriate on screen notification.

Each probe may have a unique element coordinate table which may bepermanently associated with the probe, and which may be updated insubsequent calibration processes. In some embodiments, the calibrationdata overwrites calibration data previously stored in the memory.Overwriting advantageously ensures that updated data is constantlyavailable, even in systems with small amounts of available memory.

In some embodiments, probes may be recalibrated and data stored as manytimes as desired by an operator, technician, or manufacturer.

The stored coordinate table may be used by ultrasound imaging systemelectronics in order improve the quality of ultrasound images generatedusing the calibrated probe. In one embodiment, the updated position datacan be used during imaging, e.g., the stored data can be used as aninput in an algorithm used to generate an image from a multiple apertureultrasound imaging system. In another embodiment, the stored coordinatetable can be used in post-image processing, i.e., the stored data can beused to decode stored image data or raw echo data.

Instruments of any kind used in the field on a daily basis willtypically suffer from general wear and tear. To better understand thedegradation of ultrasound transducers over time, as well as to obtainregular feedback pertaining to the general functionality of the probe,the calibration system may also be configured to perform general qualityassurance functions. In some embodiments, the calibration system maytest both the transmitting and receiving functions of the probe, reportoperational capabilities to the sonographer and send probe functionalitydata and repair requests to the service provider.

In some embodiments, the quality assurance test may be performed beforeeach calibration so that the information obtained can be used to moreaccurately calibrate the probe. In some embodiments, after securing aprobe in a docking area of the calibration system, a quality assurancetest sequence may be manually or automatically initiated. For example,in some embodiments, the quality assurance test may be initiated via abutton on the control panel. In some embodiments, a quality assurancetest sequence may comprise three stages: The first stage will bereferred to as hydrophone verification, the second stage will bereferred to as an element transmit test and the third will be referredto as an element receive test.

In some embodiments, an additional self-test hydrophone 240 may bemounted to a side wall near the top of the tank 122 for use in qualityassurance testing. The self-test hydrophone 240 and correspondingcontrol electronics may be configured to check the position and functionof the hydrophones of the main hydrophone matrix 230 in order to ensureproper calibration of the calibration system. In one embodiment theself-test hydrophone 240 may be located in the top of the tank 122 alongthe centerline of the hydrophone matrix 230. In other embodiments, aself-test hydrophone 240 may be positioned at any other location withinthe tank suitable for performing the described functions. In a processsimilar to the process for calibrating ultrasound probe elements, theself-test hydrophone 240 may send and receive ultrasound pulses to themain calibration hydrophones 230 and then use this information to ensurethe hydrophones 230 are functioning properly and accurately.

Each hydrophone of the main hydrophone matrix 230 may also transmit aself-test signal to be received by the self-calibrator hydrophone 240.The process may be similar to those described elsewhere herein for thecalibration and quality assurance testing of ultrasound probe elements.The proper functioning and exact location of the hydrophone elements isvery important for the best possible calibration of the probes.

In some embodiments, the hydrophone verification stage may ensure thatinformation obtained from the hydrophones is accurate. As shown in FIG.28, some embodiments of the calibration system may be equipped with oneor more self-calibrator hydrophones 240 located in a top corner of thetank. A self-calibrator hydrophone 240 may be used to verify thetransmitting and receiving capabilities of the hydrophones elements ofthe hydrophone arrays 810, 845, 875 in the hydrophone matrix 230. Insome embodiments, the self-calibrator may also be used to verify theacoustic positions of the elements of the main hydrophone matrix 230.The self-calibrator may transmit ultrasonic self-test signal pulse orpulses in a set pattern from a known location. The strength of receivedsignals and the order in which they are received may be used todetermine the acoustic position and receiving functionality of thehydrophone elements using methods similar to those described above.

In some embodiments, a quality assurance transmit test may be designedto test the transmit strength, efficiency and/or effectiveness of eachtransducer element of an ultrasound probe. A QA transmit test may beginby exciting a test transducer element with a precise electrical signalto cause the transducer to transmit ultrasonic pulses. The transmit testsignal may have any shape and frequency as desired, preferably with goodautocorrelation properties as discussed above with reference tocalibration test embodiments.

The test signals may then be received by one or more hydrophoneelements. The received frequency may then be transformed by thehydrophone transducer into specific amplitudes of electrical charge.From the resulting charges obtained by the hydrophones, the calibrationsystem may determine whether a received signal has expected propertiesbased on the electrical signal input to the test element. After testingall test elements, the calibration system may determine which testelements fall below an average transmitting capability and which fail tofire at all. This information may be obtained by comparing theamplitudes created by each test signal and then identifying whichelements fall below the mean and by how much. In some embodiments, QAtransmit test result data may be stored in a calibration chip within aprobe or in any other suitable location. In some embodiments, anabsolute value of a mean transmit strength may also be stored andanalyzed over time to evaluate the long term health of a probe.

In some embodiments, a quality assurance receive test may evaluate thereceiving capabilities of each probe element in a similar (but opposite)process. In some embodiments, a calibration hydrophone (230 or 240) maytransmit a precise ultrasonic test signal pulse or pulses of a knownfrequency. Each probe element may then receive the test signal andtransform it into an electrical charge with a specific amplitude. Theelectric charges or amplitudes of the receiving probe elements may thenbe compared relative to each other and to any previous receive testdata. Much like the transmitting test elements that are receiving poorlyor not converting the ultrasonic pulses at all may fall out oftolerance. The average of the element receiving pulse amplitudescompared over time may indicate the degradation of elements. As above,test data may be logged, stored, and analyzed over time.

In some embodiments an ultrasound system operator/technician may beprovided with information about quality assurance calibration and testdata resulting from the above processes. In some embodiments, a serviceprovider and/or probe manufacturer may also be informed of calibrationand/or test data, e.g., when elements are underperforming or no longertransmitting or receiving. This information can be used to decide whento schedule probe repairs or when a probe should be replaced.Compensation for elements which are no longer firing, or for theadjustment of transmit amplitude and receive gain of any particularelement may then be done internally to the electronics of an ultrasoundimaging system (e.g., MAUI electronics in the case of a multipleaperture ultrasound imaging system).

Although many of the embodiments of ultrasound probe calibration andquality assurance testing systems and methods are shown and describedwith reference to multiple aperture ultrasound imaging probes, thesesystems and methods can also be applied to single aperture ultrasoundimaging systems.

Terms such as “optimized,” “optimum,” “precise,” “exact” and similarterms used in relation to quantitative parameters are merely intended toindicate design parameters which may be controlled or varied inaccordance with general engineering principles, and may involve acompromise based on the balancing of competing design factors. Use ofthese terms is not intended to imply or require that the parameters orcomponents thereof are designed for the best possible or theoreticalperformance.

The above disclosure is sufficient to enable one of ordinary skill inthe art to practice the invention, and provides the best mode ofpracticing the invention presently contemplated by the inventor. Whilethere is provided herein a full and complete disclosure of the preferredembodiments of this invention, it is not desired to limit the inventionto the exact construction, dimensional relationships, and operationshown and described. Various modifications, alternative constructions,changes and equivalents will readily occur to those skilled in the artand may be employed, as suitable, without departing from the true spiritand scope of the invention. Such changes might involve alternativematerials, components, structural arrangements, sizes, shapes, forms,functions, operational features or the like.

What is claimed is:
 1. An ultrasound probe calibration device,comprising: a tank having a top portion, a bottom wall, at least oneside wall between the top portion and the bottom wall, an internalvolume filled with a gel or a solid filler material, and at least onetarget within the tank volume; the upper portion defining an ultrasoundprobe docking area having at least one ultrasound probe receiver and amechanical docking device configured to hold an ultrasound probe in asubstantially rigid, consistent, and immobile position.
 2. The device ofclaim 1, wherein the mechanical docking device comprises a claspconfigured to secure a handle portion of the ultrasound probe in a fixedposition.
 3. The device of claim 1, wherein the probe receiver comprisesa molded body that conforms to a shape of the ultrasound probe.
 4. Thedevice of claim 3, wherein a material of the ultrasound probe receiveris the same material as the filler material.
 5. The device of claim 4,wherein the filler material and the ultrasound probe receiver materialare both ballistics gel.
 6. The device of claim 1, wherein theultrasound probe receiver comprises a flexible fluid-filled bladder. 7.The device of claim 1, wherein the ultrasound probe docking areacomprises a plurality of molded probe receivers conforming to shapes ofdifferently-shaped ultrasound probes.
 8. The device of claim 1, whereinthe ultrasound probe receiver comprises electrical contacts arranged andconfigured to interact with corresponding electrical contacts on anultrasound probe positioned in the receiver.
 9. The device of claim 1,further comprising at least one temperature sensor in the tank.
 10. Thedevice of claim 1, wherein the target comprises a hydrophone matrix onthe bottom wall of the tank.
 11. The device of claim 10, wherein thehydrophone matrix comprises a multi-axis hydrophone including atransverse hydrophone array, a right hydrophone array, and a lefthydrophone array.
 12. The device of claim 10, wherein the hydrophonematrix comprises a two-dimensional array of hydrophone elements.
 13. Thedevice of claim 10, further comprising a self-test hydrophone on the atleast one side wall of the tank and separate from the hydrophone matrix.14. The device of claim 10, further comprising a self-test hydrophonelocated in the upper portion of the tank along a centerline of thehydrophone matrix.